Method of curing an optical disc

ABSTRACT

There is provided a method of curing an optical disc capable of effectively curing the optical disc without generating a warp phenomenon when optical disc is cured while ultraviolet curing resin material is irradiated with ultraviolet. The method of curing an optical disc comprises overlaying first and second resin substrates onto each other by way of an adhesive made of ultraviolet curing resin material, the method further comprising clamping the optical disc by ultraviolet transmittance plates at both sides thereof, and curing the adhesive while being irradiated with ultraviolet from outside of the ultraviolet transmittance plates.

This is a division of Ser. No. 08/708,079, filed Aug. 30, 1996, now U.S.Pat. No. 5,779,855.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of and an apparatus for curingan optical disc (hereinafter referred to as an optical disc curingmethod and an optical disc curing apparatus), particularly to a methodof and apparatus for curing an optical disc comprising first and secondresin substrates which are overlaid with each other by way of anadhesive.

2. Prior Art

Computers have been now used in various fields, and they have a leapforward in development of processing capacity and speed. Particularly,storage density of memories to be used has improved dramatically,impacting daily life to change a common sense in the daily life. Amongmemories, a so-called storage disc, particularly, an optical disc isconvenient to be carried and has various uses as storage means.

The optical disc is preferably formed of a discoid substrate made ofsynthetic resin such as polycarbonate.

Signal pits that are information signals, hereinafter referred to asinformation, are stored in the resin substrate, and a reflecting filmmade of aluminum or the like is formed on the resin substrate. Aprotecting resin layer made of, e.g., ultraviolet curing resin(so-called ultraviolet resin) is formed on the reflecting film forprotecting the resin substrate in which information is stored.

Whereupon, a thickness of the resin substrate is set to 0.6 mm in viewof the recording of the signal pits, the manufacturing limits, andstrength of the resin substrate.

Since a CD has a thickness of about 1.2 mm as its standard, it is veryuseful for two resin substrates to be bonded to each other by anadhesive to conform to the thickness of the CD.

An optical disc D shown in FIG. 5 typically comprises a first resinsubstrate U1 composed of a resin substrate in which information ishaving a reflection film a and a protecting resin layer b formed on thereflecting film a, and a second dummy resin substrate U2 in which noinformation is stored, wherein the second dummy resin substrate U2 isbonded to the first resin substrate U1.

An optical disc D shown in FIG. 6 comprises two resin substrates inwhich different information is stored are bonded to each other.

The optical disc D in FIG. 6 comprises first and second resin substratesU1 and U2 each composed of a resin substrate in which information isstored having a reflection film a formed on the resin substrate and aprotecting resin formed on the reflecting film a, wherein the first andsecond resin substrates U1 and U2 are bonded to each other by way of anadhesive R.

The optical disc having both resin substrates in which information isinputted is largely expected hereinafter as a digital video disc (DVD)sometimes referred to as a digital versatile disc. Whereupon, theinventors of the present application manufacture the optical disc in thefollowing manner.

FIGS. 7 (1) through (5) show schematic views for explaining theprocesses to manufacture the optical disc D by bonding two resinsubstrates. These procedures are now briefly described in the order ofthe procedures.

First, a first resin substrate U1 in which information is stored isplaced on a receiving table S (Process 1).

The receiving table S has a boss at the center thereof for positioningthe resin substrate U1 and is rotatable at high speed (a boss is omittedin FIG. 7). Successively, the first resin substrate U1 is placed on thereceiving table S, and an adhesive R such as ultraviolet curing resin,etc. on the first resin substrate U1 (Process 2).

When the ultraviolet curing resin is used as the adhesive R, coating isplaced onto the first resin substrate U1 by way of a nozzle so as topour the adhesive R therefrom onto the first resin substrate U1. Forexample, if a jet nozzle N is moved in a state where the first resinsubstrate U1 is turned, the adhesive R can be coated onto the firstresin substrate U1 in a doughnut shape. After the adhesive R is coatedonto the first resin substrate U1, the second resin substrate U2 can beoverlaid on the first resin substrate U1 (Process 3).

Thereafter, the overlaid two resin substrates are integrally turned athigh speed (Process 4).

That is, the adhesive interposed between the first and second resinsubstrates U1 and U2 is developed to extend uniformly between the firstand second resin substrates U1 and U2.

Air sealed between the first and second resin substrates are blown offin a state where both resin substrates are overlaid onto each otherduring rotation. Further, an air bubble which is contained in theadhesive per se, if any, also escapes outside the adhesive.

In the developing process, a large quantity of the adhesive R interposedbetween both resin substrates is scattered from the circumferentialperipheries of both resin substrates when the receiving table S isturned at high speed. Although the developing time is several seconds,the adhesive is strongly scattered at an acceleration time, before therotating speed is changed to a high rotating speed, namely, within oneto two seconds of several seconds of the developing time.

After the adhesive R is developed, it is cured in the next process. Whenthe ultraviolet curing resin is used as the adhesive R, the resin isirradiated with ultraviolet radiation (hereafter ultraviolet) which isirradiated from the upper portion of the second resin substrate. Whenthe ultraviolet curing resin is cured upon reception of the ultravioletso that the first and second resin substrates U1 and U2 are integratedwith each other, thereby forming a strongly bonded optical disc.

The inventors of the present application have manufactured the opticaldisc by bonding the first and second resin substrates in the manner asset forth above.

Meanwhile, when the adhesive is cured, the optical disc is placed on thereceiving table and it is irradiated with the ultraviolet from the upperportion of the optical disc, it is understood that the optical disc issubject to a warp phenomenon, namely, it is liable to be warped.

That is, if the optical disc comprises both resin substrates in whichinformation is respectively stored or even if it comprises both resinsubstrates in any of which information is stored, when the adhesive iscured when it is irradiated with the ultraviolet from, e.g., the upperportion of the resin substrates, a warp phenomenon is generated, namely,the optical disc per se is bent upward.

The optical disc which was subject to the warp phenomenon, namely, thewarped optical disc is deteriorated in quality, and hence the warpphenomenon must be avoided. On the other hand, when the optical disc ismanufactured, the curing time must be as short as possible to enhancethe productivity. Accordingly, the intensity of the ultraviolet isincreased so as to cure the adhesive. However, when the intensity of theultraviolet is increased, we found that there was a tendency that theoptical disc was largely warped. As a result, in the conventional curingmethod, there is a limit to expedite the curing speed, leading todeterioration of productivity.

SUMMARY OF THE INVENTION

The present invention has been made to solve the aforementionedproblems. That is, the inventors of the present application endeavoredthemselves to study these problems and discovered that the adhesivecould be effectively cured and the warp phenomenon is prevented if theadhesive is irradiated with ultraviolet not from one side thereof butfrom both sides thereof. Further, they discovered that the warpphenomenon was more surely prevented if the optical disc can be clampedand held by members which can sufficiently transmit light therethroughand hold the optical disc from both sides thereof. As a result, thepresent invention has been completed.

It is an object of the present invention to provide a method of and anapparatus for curing an optical disc capable of effectively curing theoptical disc without generating a warp phenomenon when the optical discis irradiated with ultraviolet to thereby cure a ultraviolet curingresin.

To achieve the above object, it is a first aspect of the invention toprovide a method of curing an optical disc comprising overlaying firstand second resin substrates onto each other by way of an adhesive madeof ultraviolet curing resin material, the method further comprisingclamping the optical disc by ultraviolet transmittance plates at bothsides thereof, and curing the adhesive while being irradiated withultraviolet from outside of the ultraviolet transmittance plates.

It is a second aspect of the present invention to provide a method ofcuring an optical disc comprising overlaying first and second resinsubstrates onto each other by way of an adhesive made of ultravioletcuring resin material, the method further comprising clamping theoptical disc by ultraviolet transmittance plates at both sides thereof,moving the optical disc between ultraviolet irradiators while theoptical disc is clamped by the ultraviolet transmittance plates at bothsides thereof, and curing the adhesive while being irradiated withultraviolet from outside of the ultraviolet transmittance plates.

It is a third aspect of the present invention to provide a method ofcuring an optical disc according to the second aspect of the invention,wherein the optical disc is horizontally turned and is moved togetherwith the ultraviolet transmittance plates.

It is a fourth aspect of the present invention to provide a method ofcuring an optical disc according to the second aspect of the invention,wherein the optical disc is moved together with ultraviolettransmittance plates while the optical disc and the ultraviolettransmittance plates are placed on a receiving platform.

It is a fifth aspect of the invention to provide an apparatus for curingan optical disc comprising first and second resin substrates, the firstresin substrate being overlaid on the second resin substrate by way ofan adhesive, two ultraviolet transmittance plates for clamping theoptical disc therebetween, a base table for supporting the twoultraviolet transmittance plates, a conveying means for moving the basetable, and an ultraviolet irradiators for irradiating the optical discon the base table with ultraviolet from both sides thereof.

It is a sixth aspect of the invention to provide an apparatus accordingto the fifth aspect of the invention, wherein the base table has adoughnut shape and a hole formed by boring a center thereof (hereinafterreferred to as a bore portion) wherein the ultraviolet irradiatorsirradiate ultraviolet which passes through the bore portion.

It is a seventh aspect of the invention to provide an apparatusaccording to the fifth aspect of the invention, wherein the conveyingmeans is a conveyor for conveying the base table while placing the basetable thereon.

It is an eighth aspect of the present invention to provide an apparatusaccording to the seventh aspect of the invention, wherein the conveyorincludes two endless belts, the two belts being differentiated invelocities thereof, and wherein the base table is turned owing to thedifference of velocities.

It is a ninth aspect of the invention to provide an apparatus accordingto the fifth aspect of the invention, wherein the ultraviolettransmittance plates are respectively formed of quartz glass.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is an enlarged perspective view showing a main portion of anoptical curing apparatus according to a first aspect of the invention;

FIG. 2 is a view for explaining rotation of an optical disc of theoptical curing apparatus in FIG. 1;

FIG. 3 is a perspective side view of the optical disc curing apparatusin FIG. 1;

FIG. 4 is a view showing positioning of the optical disc curingapparatus with reference to former and latter processes of the entireprocess of an optical disc curing method;

FIG. 5 is a view showing the optical disc where information is stored inone of resin substrates;

FIG. 6 is a view showing the optical disc where information is stored inboth of the resin substrates; and

FIG. 7 is a perspective view showing processes for manufacturing theconventional optical disc.

PREFERRED EMBODIMENT OF THE INVENTION

First Embodiment (FIGS. 1-6):

FIG. 1 is an enlarged perspective view showing a main portion of anoptical disc curing apparatus according to a first embodiment of theinvention.

The optical disc curing apparatus mainly comprises a first apparatushaving a function to irradiate ultraviolet, and a second apparatus forpermitting the optical disc to pass through an irradiation area Z wherethe optical disc is irradiated with ultraviolet.

The first apparatus comprises mainly a plurality of ultravioletirradiators 6 and a cover body 7 for surrounding the ultravioletirradiators 6, wherein an area between these irradiators 6 is called asthe irradiation area Z of the ultraviolet.

Cooling means or partition boards, not shown, may be provided inside thecover body 7 to effectively irradiate ultraviolet.

The cooling means are provided for restraining heating of theirradiators 6, for example, means for blowing cold air in the cover body7 through ventilation ports F.

The second apparatus comprises a placing/moving means disposed in theirradiation area Z of the ultraviolet.

The ultraviolet irradiators 6 irradiate ultraviolet, whereby an adhesiveinterposed between both resin substrates of the optical disc D, namely,a ultraviolet curing resin is irradiated with the ultraviolet and iscured.

Reflecting plates 6A are normally provided at the back surfaces of theultraviolet irradiators 6 for effectively irradiating the ultraviolet.

The ultraviolet irradiators 6 are appropriately disposed so that theoptical disc, which is placed on the belt conveyor, described later, canbe irradiated with ultraviolet from the upper and lower sides thereof.

The placing/moving means comprises a pair of ultraviolet transmittanceplates 1 and 2 for clamping the optical disc D, a base table 3 on whichthe ultraviolet transmittance plates 1 and 2 are placed, and a beltconveyor 4 for conveying the base table 3 while the base table 3 isplaced thereon.

The ultraviolet transmittance plates 1 and 2 are respectively formed ofmaterial which sufficiently transmits ultraviolet, for example, they arepreferable to be formed of heat-resistant plates such as quartz glassplates and PYREX (trademark) glass.

The ultraviolet transmittance plates 1 and 2 clamp the optical disc Dfrom the upper and lower sides thereof, and they preferably havediameters which are respectively the same as or slightly less thandiameter of the optical disc.

The base table 3 is a table on which ultraviolet transmittance plates 1and 2 are placed, and has a recess 3C, and it has a doughnut shape acenter of which is bored.

A reflecting member 3A is provided on the base table 3, and it reflectsthe ultraviolet and effectively cures the peripheral end portion of theoptical disc which is relatively difficult to cure.

The base table 3 may be formed by fixing a separately manufacturedreflecting member of 3A thereto or by integrally fixing the reflectingmember 3A thereto.

The lower ultraviolet transmittance plate 2 comprises a large diameterportion and a small diameter portion wherein the large diameter portionis fitted in the recess 3C of the base plate 3 so that the plate 2 issupported by the base plate 3.

The lower ultraviolet transmittance plate 2 has a boss 21 at the centerthereof for positioning the ultraviolet transmittance plate 2, and theboss 21 is preferably formed of the same material as the ultraviolettransmittance plate 2.

The upper ultraviolet transmittance plate 1 is formed in a discoid shapefor clamping the optical disc D between itself and the lower ultraviolettransmittance plate 2 utilizing its weight. It is preferable that thediameter of the upper ultraviolet transmittance plate 1 is the same asthe small diameter portion of the lower ultraviolet transmittance plate2.

If the central portion or adjacent portion thereof is pressed in anextreme way, the optical disc is prevented from being warped to someextent, there may be employed the upper ultraviolet transmittance plate1 having a small diameter capable of pressing the central portion alone.

In this case, it is also possible to use a metallic ring (made ofstainless steel sheet and having a thickness of 10 mm and an outerdiameter of 3 mm) sufficiently serving as a weight instead of the upperultraviolet transmittance plate 1 having the small diameter.

The upper ultraviolet transmittance plate 1 has a central bore portion1A through which the boss 21 of the ultraviolet transmittance plate 2 isinserted. To set the optical disc D on the base table 3, the lowerultraviolet transmittance plate 2 is first engaged in the recess 3C ofthe base table 3. Then the optical disc D is placed on the ultraviolettransmittance plate 2 while the boss 21 is inserted into the centralbore portion 1A of the optical disc D.

Successively, the ultraviolet transmittance plate 1 is placed on theoptical disc D while the boss 21 is inserted into the central boreportion 1A of the ultraviolet transmittance plate 1. In this state, theoptical disc D is clamped between the upper and lower ultraviolettransmittance plates 1 and 2 from the upper and lower sides thereof, andit is set on the base table 3. At this time, the peripheral edge of theoptical disc D slightly protrudes outside from the ultraviolettransmittance plates 1 and 2.

Since the base table 3 has the doughnut shape, the optical disc isirradiated with the ultraviolet through the bored portion 3B of the basetable 3.

Accordingly, the optical disc D is irradiated with ultraviolet from theupper side of the upper ultraviolet transmittance plate 1 and the lowerside of the lower ultraviolet transmittance plate 2, whereby it can beuniformly irradiated, and hence the warp phenomenon can be prevented.

Further since the optical disc D is clamped by the ultraviolettransmittance plates 1 and 2, the warp phenomenon is more surelypresented. On the other hand, the belt conveyor 4 is a conveying meansfor conveying the base table 3 while the base table 3 is placed thereon,and it comprises a pair of belts 4A and 4B each having small width and apair of guides 5, which are respectively spaced from each other.

The guides 5 guide and support the pair of belts 4A and 4B. The belts 4Aand 4B have respectively stepped portions, and supporting surfaces 42for supporting the base table 3 and surfaces 41 for preventing the basetable 3 from being laterally vibrated.

The belts 4A and 4B are usually set in such a manner that one of themtravels faster than the other. Accordingly, the base table 3 placed onthe belt conveyor 4 can perform rotary motion owing to the difference ofvelocities between the belts 4A and 4B when it is moved while beingsupported by the belts 4A and 4B.

FIG. 2 is a view for explaining the rotation of the base table 3.Suppose that the velocity V1 of the belt 4B is greater than the velocityV2 of the belt 4A, the base table 3 is turned counterclockwise while theoptical disc D is placed thereon.

Meanwhile, it is needless to say that the greater the difference ofvelocities, the faster the rotating velocity, and if both velocities areequal to each other, the rotating velocity becomes zero.

In the ultraviolet irradiation area Z, the optical disc D is irradiateduniformly with the ultraviolet owing to the rotary motion of the basetable 3.

FIG. 3 is a schematic side view of the optical disc curing apparatus.

In the first step, the optical disc D is clamped by the ultraviolettransmittance plates 1 and 2 from the upper and lower sides thereof andit is placed on the base table 3. In this state, the optical disc D isplaced on the belt conveyor 4 of the optical disc curing apparatus andis moved by the belt conveyor 4. Thereafter the optical disc D isconveyed at a given speed in a ultraviolet irradiation area Z surroundedby the cover body 7.

In the cover body 7, air current is generated owing to a cold air blownout from the ventilation ports F.

However, since the upper ultraviolet transmittance plate 1 is placed onthe optical disc D, the optical disc is neither blown up nor lifted up.

The optical disc D is irradiated with the ultraviolet by the pluralityof ultraviolet irradiators 6 from the upper and the lower sides thereofwhile it is conveyed. It is needless to say that the ultravioletirradiators 6 may be arranged in parallel with the moving direction ofoptical disc D although they are arranged perpendicularly with respectto the moving direction of the optical disc D.

Intensity of the ultraviolet which is irradiated vertically from theultraviolet irradiators 6 is needed to be adapted for the substratecharacteristics of the first resin substrate or the second resinsubstrate, and hence it is preferable that each of the ultravioletirradiators 6 can be adjusted so that intensity of ultraviolet adjusted.

While the optical disc D passes through the ultraviolet irradiation areaZ, the ultraviolet curing resin is gradually cured by the ultraviolet.The ultraviolet curing resin is substantially completely cured at thetime when the optical disc D passed through the ultraviolet irradiationarea Z.

Since the optical disc D is irradiated with the ultraviolet not onlyfrom one direction but also from two directions, i.e., from the upperand the lower sides thereof, it is possible to prevent the optical discD from being warped. Since the optical disc D is clamped by theultraviolet transmittance plates 1 and 2 from both sides thereof, thewarp phenomenon can be more effectively prevented.

FIG. 4 shows an optical disc curing apparatus A which is illustratedwith association of former and latter processes of the optical disccuring method. An optical disc manufacturing apparatus B is disposed infront of the optical disc curing apparatus A for performing processesbefore the ultraviolet curing resin of the optical disc is cured.

The optical disc manufacturing apparatus B performs the processes 1through 4 as explained in FIG. 6. That is, the processes of placing thefirst resin substrate on the receiving table, applying the adhesive onthe first substrate, overlaying the second resin substrates onto thefirst substrate, and developing the adhesive, etc.

Although the optical disc D is supplied from the optical discmanufacturing apparatus B to the optical curing apparatus A, the opticaldisc D is delivered to the optical curing apparatus A while it isclamped by the ultraviolet transmittance plates 1 and 2 and held on thebase table 3. After the optical disc D is completely cured by theoptical curing apparatus A, it is moved to the next process by theconveyor body, then the upper ultraviolet transmittance plate 1 isremoved from a lateral moving take up chuck 8. The removed ultraviolettransmittance plate 1 is bypassed from the main stream of the processand is also conveyed in front of the optical disc manufacturingapparatus B by another conveyor body.

The optical disc D is taken out by a rotary motion take out chuck 9 fromthe upper portion of the base table 3 from which the ultraviolettransmittance plate 1 is removed. The thus taken out optical disc isdelivered to a test table C1. In the test table C1, the optical disc issubject to a given test, and then the tested optical disc isaccommodated into a stack of an accommodation table C2.

Thereafter, the optical disc D is taken out from the stack and isconveyed to a portion where a casing process, not shown, is performed.

On the other hand, the base table 3 from which the optical disc D istaken out (in a state where the lower ultraviolet transmittance plate 2is engaged in the base table 3) is transferred to the optical discmanufacturing apparatus B, where a new optical disc is placed on thetransferred base table 3 by way of a rotary motion take out chuck 10.

The upper ultraviolet transmittance plate 1, which was taken out fromthe optical disc D by the lateral moving take up chuck 8 in the previousprocess and conveyed to the optical disc manufacturing apparatus B whileit was bypassed, is placed on the new optical disc by way of a lateralmoving take up chuck 11. The new optical disc is delivered to theoptical curing apparatus A, when the new optical disc is subject to theultraviolet curing process.

The aforementioned processes are repeated.

It is needless to say that the present invention is not limited to theaforementioned embodiment but it can be modified variously to an extentnot to deviate from the scope of the invention.

For example, the shape and the number of the ultraviolet irradiators canbe varied freely. Further, the shapes of the ultraviolet transmittanceplates are not limited to a discoid one but they may be of any shape ifthey can clamp the optical disc.

As mentioned in detail above, the present invention can prevent the warpphenomenon and effectively cure the optical disc.

What is claimed is:
 1. A method of bonding optical disc substrates to create an optical disc including first and second overlaid substrates having an adhesive made of ultraviolet curing resin material interposed therebetween, said method comprising:clamping said overlaid optical disc substrates between ultraviolet transmittance plates provided at both sides thereof, and curing said adhesive by irradiating same with ultraviolet from outside of said ultraviolet transmittance plates.
 2. The method of bonding substrates according to claim 1, wherein the step of curing includes reflecting irradiation toward the periphery of the optical disc substrates so as to cure the periphery of the adhesive.
 3. The method of bonding substrates according to claim 1, wherein the step of curing includes the step of moving said optical disc substrates past irradiators so as to expose said adhesive to the irradiation.
 4. The method of bonding substrates according to claim 3, wherein the step of moving includes simultaneously rotating said optical disc substrates as the substrates are moved past the irradiators so as to uniformly expose the adhesive to the irradiation.
 5. The method of bonding substrates according to claim 1, wherein the step of curing includes supporting the overlaid substrates on adjacent first and second belts, and moving said belts at one of a same velocity so as to nonrotatably move the overlaid substrates past irradiators for curing the adhesive and differing velocities so as to simultaneously rotate and move the overlaid substrates past irradiators for curing the adhesive.
 6. The method of bonding according to claim 1, wherein the step of curing includes transmitting at least some of the ultraviolet through the transmittance plates.
 7. A method of bonding optical disc substrates to create an optical disc including first and second overlaid substrates having an adhesive made of ultraviolet curing resin material interposed therebetween, said method comprising:clamping said overlaid optical disc substrates between ultraviolet transmittance plates provided at both sides thereof; moving said optical disc substrates between ultraviolet irradiators while said optical disc substrates are clamped between said ultraviolet transmittance plates; and curing said adhesive by irradiating same with ultraviolet from outside of said ultraviolet transmittance plates.
 8. A method of bonding optical disc substrates according to claim 7, wherein said optical disc substrates are horizontally turned and moved together with said ultraviolet transmittance plates.
 9. A method of bonding optical disc substrates according to claim 7, wherein said optical disc substrates are moved together with said ultraviolet transmittance plates while said optical disc substrates and said ultraviolet transmittance plates are placed on a receiving platform.
 10. The method according to claim 7, wherein the ultraviolet is supplied from the irradiators and at least some of said ultraviolet is transmitted through the transmittance plates.
 11. The method of bonding according to claim 7, wherein the steps of curing includes reflecting irradiation toward a periphery of the optical disk substrates so as to cure the periphery of the adhesive. 